1. Field of the Invention
This invention relates to composite manufacturing. Particularly, this invention relates to techniques for impregnating composite fibers with viscous resins.
2. Description of the Related Art
Some existing techniques for de-gassing viscous curable fluids in manufacturing, e.g. as may be used in composite manufacturing, employ a vacuum or a centrifuge, or a combination of the two. The vacuum process has the disadvantage of boiling off important solvents from the liquid as air is removed. Elimination of such solvents creates extra expense, and the solvents may be needed in the liquid resin. For example, styrene is a solvent in thermosetting polyester resin that becomes part of the resin when it is cross linked. On the other hand, a centrifuge does not boil off solvents, but centrifuge equipment is expensive even in its simple form, such as for batch processing. Some known techniques of composite impregnation can be described.
A first technique for composite impregnation involves dipping the fibers in a bath and squeezing out the excess through a bushing or calendering rolls. This first technique is used for pultrusion, filament winding, and prepreg manufacturing, and certainly many other processes.
A second technique for composite impregnation involves allowing the fibers to settle into the liquid over time. This second technique is used in fiber reinforced plastic (FRP) panel manufacture. For FRP panel manufacture, a liquid, typically polyester resin, is metered onto a carrier film in a thin layer, and chopped fibers are dropped onto it and/or a fiberglass mat is dispensed into it. The film with resin and fiberglass is dragged over a long heated bed, where the fibers and/or fiberglass mat settle into the resin layer and are wet out by it. At the end of the heated bed, a top film is pressed onto it with nip rolls and excess resin is squeezed out. A similar third technique, also used in FRP panel manufacture, involves fibers being gently pushed into the resin with grooved or mesh surfaced rolls in contact with the materials.
A fourth technique for composite impregnation involves mechanically forcing the fibers into the liquid resin. For example, this technique is used for manufacturing prepregs with continuous fibers and hot-melt resin. In it, a release paper is coated with hot-melt resin, and a thin row of fibers is brought in with an opposing release paper and pressed into the resin-coated lower paper. Precision-ground heated rollers are used in this process, and the material is usually worked several times with these rolls to achieve wetout and B-Staging, a preliminary curing stage. Production speed is slow.
A fifth technique for composite impregnation involves working the resin material between two plastic sheets under pressure with grooved rollers or with a dual-wire-mesh compaction device. This technique is used to make sheet molding compound (SMC). An example dual-wire-mesh compaction device conveys the resin material under pressure in a serpentine path under and over processing rollers to wet out the material.
A sixth technique for composite impregnation is used in TMC Manufacture or Heinzmann technology. Examples of these processes are described in U.S. Pat. No. 3,932,980 to Mizutani and U.S. Pat. No. 4,889,429 to Heinzmann, and are used to make materials very much like SMC. These methods use rotating cylinders to bring the resin matrix and the charge together and impregnate them in a gap between the rotating cylinders. These techniques scrape or fling off the composite from the wetout rollers.
None of the existing techniques for composite impregnation differentially exclude air with positive pressure applied to a resin matrix.
In view of the foregoing, there is a need in the art for apparatuses and methods for efficiently excluding air from a resin in composite manufacturing. In addition, there is a need for such apparatuses and methods to operate with more viscous resins. There is also a need for such apparatuses and methods to provide the option of eliminating a carrier film (such as used in the sixth method, described above) to reduce production costs. There is further a need for such systems and apparatuses to be cheaper and operate at higher production rates than existing systems. These and other needs are met by the present invention as detailed hereafter.